Gas-supersaturation induced in tissues and blood during certain conditions of hypo- and hyperbaric decompression can cause gas bubbles to form with serious medical consequences. The broad objective of our present studies is to gain a better understanding of the early etiology of the air embolism, specifically with respect to how the bubbles form, where they form at the molecular, cellular and organ levels, and which factors affect the process. Several aspects of the gas bubble nucleation process will be investigated in erythrocytes and other cells from blood, in various unicellular organisms, and in simple multicellular organisms. It is of particular interest to determine the gas supersaturations that are required for the spontaneous nucleation of bubbles in intact cells and to possibly identify intra and extracellular components that may lower the cavitation stability. The methods to be used involve equilibration of the cell suspension at high gas pressures, followed by rapid or slow decompression to atmospheric pressure. The events during decompression will be monitored by a specially developed cinemicrographic technique which allows the cells to be observed at 500X magnification at pressures up to 400 atm, and recorded on 16mm film at rates up to 256 frames per second. Post-decompression examinations of the cells including variability determinations, investigations of bubble nucleation in liquids and liquid/liquid interface systems will be continued.